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Old 02-21-2019, 12:57 PM   #41
TJTx
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IMHO, like a lot of controversial subjects, it is “all of the above”.
Yes, a majority of ST tires are made in Asia/China.
Yes, too many RV’ tires are either overloaded or under-inflated.
Yes, there are user errors and/or neglect.
And on and on.
Again, IMHO, I recommend:
Research at least until you see a pattern for the best tire for you.
Follow the manufacturer’s quidelines for bothe the tires and RV.
Maintain your RV including suspension and tires.
Drive sanely. I stay in the right-most lane as much as possible unless I am forced to pass or there is a left exit. I also stay at 65 or less when there is a 70/75 speed limit or less.
Use a TPMS system as tire failure most often begins on the inside with usually no outwardly visible signs of trouble.
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Old 02-21-2019, 04:06 PM   #42
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There are two NHTSA approved procedures for displaying a ST tire's speed rating on its sidewall. In the first picture, the tire manufacturer has chosen to use the speed letter "L" and explain its rating - 75 MPH. In the second picture, the tire manufacturer has chosen the most standard way to display the speed letter "L"; at the end of a service description; 129/125 L which relates to a speed rating of 75 MPH.

When there are no speed restrictions to be found on the sidewall of a ST tire, the speed rating reverts to the Tire & Rim Association (TRA) standard of 65 MPH.


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Old 02-22-2019, 09:17 AM   #43
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If anyone is comfortable in trusting the RV industry's decision for a particular tire on their RV that is asked to perform at near 100% capacity, then by all means enjoy them. When I see you on the side of the road I will probably pull over and give you a hand.

Me on the other hand will "upgrade" my RV tires to have plenty of capacity left since roads are not perfect and we sometimes need our tires to perform better than "just barely".
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Old 02-22-2019, 10:48 AM   #44
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Interestingly, Trailer King RST ST225/75R-15 LRE and Carlisle Radial Trail HD ST225/75R-15 LRE both have M speed ratings (81 mph). I think 81 mph might be pushing it for my old 96 F250 with drum brakes. I always keep it under 65 mph (I am also not a spring chicken with lightening reflexes). The Trailer King is $75.79 a tire (plus add ons) and the Carlisle is $115.99 (both priced at Walmart for comparison). I think a difference would be the Carlisle factory may have more quality oversight from a US based company where Trailer King? Who knows how much quality control oversight? I am not a tire engineer either and since I know squat about such things, read this stuff on this forum and err on the side of safety and use tires recommended by those that seem to make the most sense.
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Old 02-22-2019, 11:23 AM   #45
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Originally Posted by wiredgeorge View Post
Interestingly, Trailer King RST ST225/75R-15 LRE and Carlisle Radial Trail HD ST225/75R-15 LRE both have M speed ratings (81 mph). I think 81 mph might be pushing it for my old 96 F250 with drum brakes. I always keep it under 65 mph (I am also not a spring chicken with lightening reflexes). The Trailer King is $75.79 a tire (plus add ons) and the Carlisle is $115.99 (both priced at Walmart for comparison). I think a difference would be the Carlisle factory may have more quality oversight from a US based company where Trailer King? Who knows how much quality control oversight? I am not a tire engineer either and since I know squat about such things, read this stuff on this forum and err on the side of safety and use tires recommended by those that seem to make the most sense.
The recent requirement imposed on ST tire manufacturers to provide a speed rating for their tires is very beneficial to all users. Speed ratings are directly related to tire fatigue. Not many years ago all ST tires were speed restricted to 65 MPH or less.

At a driving speed of 65 MPH, a tire rated for 65 MPH is providing 100% of its maximum load capacity. As the speed ratings are increased, less and less of that 100% is used.

Many will argue that the ST manufacturers just put speed letters on the tires to satisfy the requirement. If so they committed mail fraud because they had to tell NHTSA the tires were tested.
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Old 02-22-2019, 04:15 PM   #46
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Originally Posted by CWtheMan View Post
The recent requirement imposed on ST tire manufacturers to provide a speed rating for their tires is very beneficial to all users. Speed ratings are directly related to tire fatigue. Not many years ago all ST tires were speed restricted to 65 MPH or less.

At a driving speed of 65 MPH, a tire rated for 65 MPH is providing 100% of its maximum load capacity. As the speed ratings are increased, less and less of that 100% is used.

Many will argue that the ST manufacturers just put speed letters on the tires to satisfy the requirement. If so they committed mail fraud because they had to tell NHTSA the tires were tested.

I am not aware of where the table is and test requirements are for the various Speed Symbol letters in FMVSS 119, 120 or 139. Could you educate us please.It is my understandnig that the speed rating was added in response to FTC "anti-dumping" tariffs imposed on non-speed rated tires a couple years ago. IMO the speed ratings seem a bit arbitrary and some appear to possibly be unrealistic.
SAE has speed test specifically for passenger tires. You might review that test requirement and let us know if you feel that is reliable to predict use of a tire that has it's load calculated based on 65 mph speed limit.
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Old 02-22-2019, 08:56 PM   #47
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Originally Posted by Tireman9 View Post
I am not aware of where the table is and test requirements are for the various Speed Symbol letters in FMVSS 119, 120 or 139. Could you educate us please.It is my understandnig that the speed rating was added in response to FTC "anti-dumping" tariffs imposed on non-speed rated tires a couple years ago. IMO the speed ratings seem a bit arbitrary and some appear to possibly be unrealistic.
SAE has speed test specifically for passenger tires. You might review that test requirement and let us know if you feel that is reliable to predict use of a tire that has it's load calculated based on 65 mph speed limit.

NHTSA is not going to allow speed letters on a tire's sidewall without some form of certification from their manufacturers. Here's the short version.

"Speed ratings are determined through laboratory tests. Although this is an over simplification of the actual test procedure, essentially a tire is pressed against a large diameter metal drum to simulate its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10-minute increments) until the tire’s required speed has been met, or the tire fails."
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Old 02-23-2019, 02:07 PM   #48
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NHTSA is not going to allow speed letters on a tire's sidewall without some form of certification from their manufacturers. Here's the short version.

"Speed ratings are determined through laboratory tests. Although this is an over simplification of the actual test procedure, essentially a tire is pressed against a large diameter metal drum to simulate its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10-minute increments) until the tire’s required speed has been met, or the tire fails."

Still can't find the test procedure for the various SAE speed symbols in FMVSS.


Where in FMVSS regulations did you find the statement on speed ratings that you quoted?


Yes NHTSA does have "high Speed" tests but the duration is short and I cannot find different test procedures for L, M, S, T H etc speed ratings in their requirements.


Your quote might be from SAE but they are not a regulatory agency as DOT is. Also SAE specifically states that their speed ratings are intended for passenger car tires only.
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Old 02-23-2019, 02:33 PM   #49
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Originally Posted by Tireman9 View Post
Still can't find the test procedure for the various SAE speed symbols in FMVSS.


Where in FMVSS regulations did you find the statement on speed ratings that you quoted?


Yes NHTSA does have "high Speed" tests but the duration is short and I cannot find different test procedures for L, M, S, T H etc speed ratings in their requirements.


Your quote might be from SAE but they are not a regulatory agency as DOT is. Also SAE specifically states that their speed ratings are intended for passenger car tires only.

That's from a long NHTSA interpretation file.

Everything the tire manufacturer puts on the tire sidewall must be reported and accounted for in documentations before they can put the DOT on there.
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Old 02-23-2019, 03:57 PM   #50
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Tireman9, I still remain confused that ST tires for years got their higher weight ratings based on the 65 MPH speed restriction, and now those speed restrictions have been pushed aside. As a retired tire engineer, can you tell us what changed?
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Old 02-26-2019, 08:39 AM   #51
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Tireman9, I still remain confused that ST tires for years got their higher weight ratings based on the 65 MPH speed restriction, and now those speed restrictions have been pushed aside. As a retired tire engineer, can you tell us what changed?

As I have pointed out I can find no clear indication of the inclusion of some "magic" rubber or other feature" that is used exclusively in ST tires that allow them to carry more load than "premium" P and LT type tires.


I have asked a number of times but so far all I get is evasion or "We just made the tires better"


If that is the case then why don't numerous tire companies put this "new" "better" construction feature in their regular tires and increase the laod rating by a few hundred pounds?


While I can accept that it is possible to improve on older ST constructions to improve tire life, I can't get an answer to why don't you make a similar improvement to your line of LT tires?
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Old 02-26-2019, 09:14 AM   #52
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Originally Posted by Tireman9 View Post
As I have pointed out I can find no clear indication of the inclusion of some "magic" rubber or other feature" that is used exclusively in ST tires that allow them to carry more load than "premium" P and LT type tires.


I have asked a number of times but so far all I get is evasion or "We just made the tires better"


If that is the case then why don't numerous tire companies put this "new" "better" construction feature in their regular tires and increase the laod rating by a few hundred pounds?


While I can accept that it is possible to improve on older ST constructions to improve tire life, I can't get an answer to why don't you make a similar improvement to your line of LT tires?
Roger, here is a link to the old RV.net post about the difference in testing standards between tire types. I do not know if these standards are the same today.

https://forums.goodsamclub.com/index...9.cfm#23229249
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Old 02-26-2019, 09:20 AM   #53
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Roger, here is a link to the old RV.net post about the difference in testing standards between tire types. I do not know if these standards are the same today.

https://forums.goodsamclub.com/index...9.cfm#23229249

Yes the test requirements for P and LT tires were "upgraded" in 2002 and tires had to improve to meet the new requirements.


ST tires however still have the same 1970 test requirements for DOT




Speed Symbol testing is specified by SAE. Their test specifically states it is intended for passenger car tires. It is a 30 min step speed test. So to pass you only need to run 30 min at 88% load and not fail to pass.
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Old 03-12-2019, 08:42 AM   #54
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I am looking for some info on tire inflation. I had Trailer Kings ST205-75-14 - Load C that had maximum rating of 50 psi, which I maintained. I upgraded to Goodyear Endurance of same size which have Load D with a maximum rating of 65 psi. My dual axle trailer has a dry weight of 4300# and cargo carry capacity of 2230#, which is way more than I use. My question is what pressure should I keep tires inflated at as not to create a hard ride, but not soft to increase heat in tire. I'm not sure what my alloy rims are capable of but high pressure valve stems were installed.
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Old 03-12-2019, 09:12 AM   #55
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I am looking for some info on tire inflation. I had Trailer Kings ST205-75-14 - Load C that had maximum rating of 50 psi, which I maintained. I upgraded to Goodyear Endurance of same size which have Load D with a maximum rating of 65 psi. My dual axle trailer has a dry weight of 4300# and cargo carry capacity of 2230#, which is way more than I use. My question is what pressure should I keep tires inflated at as not to create a hard ride, but not soft to increase heat in tire. I'm not sure what my alloy rims are capable of but high pressure valve stems were installed.
your trailer should have a placard somewhere on the outside that indicates the suggested inflation pressure for the OEM tires (often this will be the same as the max inflation pressure on the tire sidewall because trailer manufacturers rarely install tires that give you any "breathing room" on load carrying capacity). The number on that placard is the lowest pressure you should run. The max inflation pressure on the new (load range D) tires is the highest you can safely run. Anywhere in between those 2 numbers is the range you have to play with, basically trading off extra carrying capacity headroom for a more compliant ride. So in your case anywhere between 50-65psi.

Have you ever weighed your trailer at a cat scale to determine how much weight is actually riding on the tires? Once you do that, you can determine how much headroom you had with the OEM Load range C tires. If the OEM tires were close to being maxed out, you should probably run toward the higher end of the range (closer to 65), but if you had tons of headroom with the OEM tires and you like the way the trailer rode at 50psi, you probably don't need to run much more than that.

Giving yourself some headroom on the carrying capacity is a good idea safety wise because tires lose some carrying capacity as they age, and our loads aren't always distributed perfectly evenly, but it's possible to go overboard on this to point where your trailer rides like the tires are made of solid rock.

There are people on these forums that will insist you must always run the max inflation pressure indicated on the tire sidewall, but that definitely isn't necessary, and in some cases (such as going up one or more load ranges when you replace the OEM tires) may give your trailer a very rough ride. It certainly did when I installed load range G sailuns on my trailer and ran them at the tires's max inflation pressure of 110psi. I typically run 90-95 (the trailer placard suggested inflation pressure for the OEM load range E Trailer Kings was 80 psi).

As you mentioned, you definitely need to verify that your rims are designed to handle the higher pressure.
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Old 03-12-2019, 09:54 AM   #56
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The inflation on a tire sidewall is the MINIMUM inflation pressure needed to support the MAXIMUM load (aosomolded o the tire sidewall).
There is a sound scientific reason to run higher inflation whe running tires on multi-axle trailers. It is called "Interply Shear". This force is what can result in belt/tread separtions. I have covered this in detail along with references to technical papers on the topic.
IMO you need a minimum of 15% "head-room" of load capacity over the leasuredload of the heavier end of an axle. (CAT scale only geves the total on an axle and very few RVs have 50/50 load split. Some oflks have discovered unbalance of 500 to 1,000#)
Most cars come with 20% to 40% tire load capacity headroom. I run 25% on my Class-C.
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Old 03-12-2019, 11:20 AM   #57
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The inflation on a tire sidewall is the MINIMUM inflation pressure needed to support the MAXIMUM load (aosomolded o the tire sidewall).
There is a sound scientific reason to run higher inflation whe running tires on multi-axle trailers. It is called "Interply Shear". This force is what can result in belt/tread separtions. I have covered this in detail along with references to technical papers on the topic.
IMO you need a minimum of 15% "head-room" of load capacity over the leasuredload of the heavier end of an axle. (CAT scale only geves the total on an axle and very few RVs have 50/50 load split. Some oflks have discovered unbalance of 500 to 1,000#)
Most cars come with 20% to 40% tire load capacity headroom. I run 25% on my Class-C.
so if a given pressure (below the tire's maximum) still provides the necessary headroom over the measured load, it's okay to run it, correct? Or am I not understanding something?
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Old 03-12-2019, 11:58 AM   #58
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so if a given pressure (below the tire's maximum) still provides the necessary headroom over the measured load, it's okay to run it, correct? Or am I not understanding something?

I wish it were that simple but all radial tires have the Interply Shear force. It's a question of how much "tire life" is being "used up". The force results in microscopic cracks forming between the two steel belts at the outer edge. Once cracks form they do not repair themselves but can only grow.

No good tool or math model can turn Shear Force into Miles of tire life is "consumed" as there are just too many variables.


Finite Element models simply indicate that higher inflation can result in lower shear force every time you turn a corner or every time a tire completes a revolution.

About the best you can do is to do a close visual inspection (Free Spin) to look for signs or out of round or side to side runout which are strong indicators of internal structural tears. I have a video and pictures of the autopsy I did on a tire where you can see the separations running across 50% to 70% of the tread width. This large separation might run a thousand miles or under certain circumstances might fail tomorrow.


Think of it like your Blood Pressure. Higher is worse. So the question is at what number can you expect to have a fatal attack?


If you consult your owner's manual you will see a suggestion that 3 to 5 years is the max expected life but obviously someone that runs at or above Max Load and above 65 mph and drives 4,000 mi a year is more likely to suffer a failure than someone that only drives 2,000 mi, never faster than 62 and at only 80% of tire load capacity.


Moving up one Load Range C>D or D>E can probably expect longer tire life if they also go from 50 to 65 or 65 to 80 psi. Going to LR-G in a Commercial grade all-steel tire should result in longer life even if you don't run 110psi.


Since load capacity is shown in the Load/Infl tables then I would suggest trying to get to 20 to 25% Reserve Load would be a good move. You still need to watch max speed and minimize sharp turns (as seen when backing) and of course, do a good free spin inspection once a year or once every 2,000 mi whichever comes first. Plus run a TPMS to confirm you never run lower pressure than your goal.
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Old 03-12-2019, 01:21 PM   #59
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This is just my opinion and experience, take it for what it is worth.
If rims are capable, and they should be if tire store mounted the new tires???? I would inflate to max stated on sidewall . Less rolling resistance, better fuel mileage, lower tire temps and less scuffing in tight turns causing less frame and suspension stress. ++++ Extra carrying capacity is a plus as long as you stay a safe margin under specs.

Make up your own mind .... common sense or technical babble.
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Old 03-12-2019, 01:47 PM   #60
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It is a stretch of the imagination to accept that we have any tire experts on this forum. We have trailer owners who offer their opinions on various issues. They share what they have learned from their experiences.

Take everything with a grain of salt. It'll taste better.
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